1. Field of the Invention
The invention relates generally to communications in a wireless network. More particularly, various embodiments pertain to determining a size of a sleep area in a wireless network supporting broadband wireless communications.
2. Background Art
Various broadband wireless communications standards such as WiMAX (e.g. the Institute of Electrical and Electronics Engineers (IEEE) 802.16e-2005 standard, released Feb. 28, 2006) incorporate the concept of a “sleep mode”. In a wireless network supporting such a standard, a base station (BS) servicing a particular geographic area may belong to a group of one or more BSs, referred to herein as a “sleep group” (SG), where the respective geographic areas of the one or more BSs define a “sleep area” (SA) of the sleep group. During an active traffic exchange, a mobile station (MS) serviced by the wireless network may be registered with (e.g. connected to) a particular BS of the geographic region in which the MS operates. The BS with which a MS is currently registered is referred to herein as a serving BS (SBS).
A sleep mode MS may maintain an association with its serving BS in order to send/receive traffic successfully. This association may consist of both static and dynamic information and states. By way of example, static information may include an MS's authentication and security credentials and/or information about an MS's service flows and connections. Some examples of static states may include an MS's data path from an Access Service Network (ASN) gateway to its serving BS. On the other hand, some examples of dynamic information include an MS's channel quality indicator (CQICH), an MS's transmission power and transmission delay parameters. Similarly, some examples of dynamic states may include states related to Automatic Repeat Request (ARQ) and hybrid ARQ (HARQ) operations etc. An SBS may assign a sleep ID (SLPID) to the MS when the MS transitions to a sleep mode from an active mode. The scope of the SLPID may be limited to coverage of the serving BS. Thus, when the sleep mode MS moves to the coverage area of another BS, it may be assigned a different SLPID. SLPID may be used to uniquely identify different sleep mode MSs within the coverage area of a particular BS.
When an MS and its SBS do not exchange traffic, there may be no need to maintain dynamic information and states for the MS. Sleep mode operation exploits this fact by putting the user into a low power operating mode in the absence of traffic exchange between an MS and its serving BS. In the absence of an active traffic exchange, the MS may switch to operating in a sleep mode to minimize MS power consumption and to decrease the usage of air interface resources. For example, a sleep mode MS may alternate between availability intervals (AI) and unavailability intervals (UAI). During an unavailability interval an MS may power down its radio interface(s). On the other hand, during availability interval the sleep MS listens for any traffic indicator message sent by its SBS to indicate the presence of traffic. The SBS may indicate the presence or absence of traffic for a sleep mode MS by sending a traffic indicator, referred to herein as a MOB_TRF-IND message, during an AI of the MS.
When an MS in active mode moves from the coverage area of its serving BS to the coverage area of another BS (referred to herein as a target BS), it may perform a handoff (HO) from its serving BS to the target BS. During the HO, the MS's static information and states may be transferred from the serving BS to the target BS. Moreover, as a part of handoff process, the MS may establish its dynamic information as well as states with the target BS. As mentioned earlier, dynamic information and states are not maintained for an SS in sleep mode. Thus, only static information and states are maintained for an SS in sleep mode. As long as the sleep mode SS resides in the coverage area of its serving BS's sleep group, no action is required to maintain its static information and states. However, when the sleep mode SS moves beyond the coverage area of its serving BS's sleep group, uncontrolled handoff (UHO) may be performed—e.g. to transfer only MS static information and/or states to the target BS. After successful completion of an UHO, the target BS may assign a new SLPID to the sleep mode MS.
Both air-link signaling messages (e.g., messages variously exchanged between the MS and its SBS and/or target BS) as well as backbone signaling messages (e.g., messages variously exchanged between an SBS and a target BS and/or other entities of a wireless communication network) may be used during a UHO. The generation, transmission, reception and/or processing of air-link signaling messages and/or backbone signaling messages results in consumption of resources of the wireless network. Limited network resources may result in a limited ability to implement a sleep mode for an MS and/or otherwise impact wireless network performance.